There is known a technique for detecting that a brake lamp provided in a vehicle is in the condition of not being able to be lighted due to burnout of the lamp or a failure in a lamp drive circuit (see Patent Literature 1).
In the above technique of Patent Literature 1, a failure in the circuit or the like is determined to electrically detect a failure, and hence it is not possible to confirm whether or not lighting of the brake lamp can actually be visually recognized from the outside.